Valve actuators are used to operate valves and are manufactured in numerous shapes, sizes, forms, and have a wide variety of utilities. Valve actuators may be manually driven, electrically driven, operated by fluid pressure in which the shaft is connected directly or indirectly to a fluid operated piston, or other hydraulic systems.
A control system, or at least a portion thereof, is often positioned on the exterior housing of a valve actuator for controlling flow through a valve to which the valve actuator is connected through a human-machine interface (HMI). Such control systems enable a user to control various functions and configurations of the valve actuator, run diagnostics on the valve actuator, and check the status of the valve actuator.
Generally, such control systems have control inputs, such as knobs, that are mechanically operated to interface with the control system of the valve actuator. In some instances, a non-contact control input, such as magnetic knobs, enables the use of external knobs while the control system is sealed inside the valve actuator. In such a configuration, rotation of one or more magnets within the magnetic knobs alters a magnetic field produced by the knobs. A sensor, such as a Hall effect sensor within the valve actuator, senses the changes in the magnetic field of the knobs and provides corresponding input signals to the control system. Such configurations may be particularly useful in environmental conditions where the exterior of the valve actuator is subjected to wet environments where fluid or other contaminants may access the internal components of the valve actuator through a direct mechanical connection, such as through the shaft of a potentiometer.
However, a non-contact mechanical connection such as magnetic knobs may still have limitations. For example, the distance between the magnets in the knobs and the Hall effect sensors within the valve actuator must be tightly controlled such that the sensor can detect movement of the knobs. If the distance grows too far, then the sensors will not detect the magnets in the knobs. Furthermore, such magnetic knobs are generally required to move through a well-defined arc in order for the rotation to be sensed. Accordingly, special care must be taken in design and in operation to ensure that no contaminating material, such as water and ice, will build up on the moveable surface that could inhibit knob motion through its full designed arc. Further still, the magnetic sensors that can detect motion only along the well-defined arc limit the functionality of the knobs.
Finally, to prevent the knobs from moving inadvertently due to vibration or other unintended physical inputs, the knob may be required to be fitted with robust springs and detents to reduce the chances of inadvertent movement of the knobs. However, such robust springs and detents require the user to exert relatively strong forces on the knobs to move them. Accordingly, such forcing of the knobs may result in a degree of discomfort after configuring one or more actuators that may each require a significant number of knob movements to complete a configuration of the valve actuator. Furthermore, the springs and detents in the knobs may fail, thereby allowing the knobs to move by gravity or vibration to some unexpected position, which in turn may place the actuator into some unexpected operating mode.